Scheduling data transmissions to improve power efficiency in a wireless network

ABSTRACT

Various embodiments are disclosed relating to scheduling data transmissions to improve power efficiency in a wireless network. In an example embodiment, uplink transmissions may be scheduled after the downlink transmissions within the frame sequence. One or more nodes having only scheduled downlink transmissions during the frame sequence may be scheduled for downlink transmissions at or near the start of the downlink transmissions. In another embodiment, one or more nodes having only scheduled uplink transmissions during the frame sequence may be scheduled for uplink transmissions at or near the end of the uplink transmissions. In yet another embodiment, one or more nodes having scheduled both downlink and uplink transmissions during the frame sequence may be scheduled for transmissions near a transition from downlink to uplink transmissions.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of, and claims priority to, U.S.application Ser. No. 11/452,082, filed on Jun. 13, 2006, entitled“SCHEDULING DATA TRANSMISSIONS TO IMPROVE POWER EFFICIENCY IN A WIRELESSNETWORK”, which, in turn, claims priority to U.S. ProvisionalApplication No. 60/691,220, filed on Jun. 16, 2005, entitled “SCHEDULINGAND SEQUENCING OF DATA AND INFORMATION FOR MAXIMAL POWER EFFICIENCY INAGGREGATED FRAMES”, both of which are hereby incorporated by referencein their entirety.

This application is related to U.S. Provisional Application No.60/620,246, filed on Oct. 19, 2004, entitled “SCHEDULING AND SEQUENCINGOF DATA AND INFORMATION FOR MAXIMAL POWER EFFICIENCY IN AGGREGATEDFRAMES”, which is hereby incorporated by reference.

BACKGROUND

The rapid diffusion of Wireless Local Area Network (WLAN) access and theincreasing demand for WLAN coverage is driving the installation of avery large number of Access Points (AP). The most common WLAN technologyis described in the Institute of Electrical and Electronics EngineersIEEE 802.11 family of industry specifications, such as specificationsfor IEEE 802.11b, IEEE 802.11g and IEEE 802.11a. A number of different802.11 task groups are involved in developing specifications relating toimprovements to the existing 802.11 technology.

Power consumption and battery life are issues for wireless devices. Anumber of power-saving techniques have been proposed to reduce powerconsumption and improve battery life. However, current techniques havenot sufficiently addressed the issue of power consumption norsufficiently reduced the number of on/off transitions to low power statefor wireless devices.

SUMMARY

Various embodiments are disclosed relating to scheduling of datatransmissions for power save delivery in a wireless network.

According to an example embodiment, a method is provided. The method mayinclude transmitting a frame including a schedule identifying uplinkand/or downlink transmission periods during a frame sequence for one ormore nodes in a wireless network. The uplink transmissions may bescheduled after the downlink transmissions within the frame sequence,with one or more nodes having only scheduled downlink transmissionsduring the frame sequence being scheduled for downlink transmissions ator near the start of the downlink transmissions. In an exampleembodiment, the transmitted frame may be a Power Save Multi Poll (PSMP)message, for example, and the frame sequence may be, for example, a PSMPsequence. In yet another example embodiment, the transmitted frame maybe, for example, an IEEE 802.11n Power Save Multi Poll (PSMP) message.

In another example embodiment, a method is provided. The method mayinclude transmitting a frame including a schedule identifying uplinkand/or downlink transmission periods during a frame sequence for one ormore nodes in a wireless network. The uplink transmissions may bescheduled after the downlink transmissions within the frame sequence.One or more nodes having only scheduled uplink transmissions during theframe sequence may be scheduled for uplink transmissions at or near theend of the uplink transmissions.

In yet another embodiment, a method is provided. The method may includetransmitting a frame including a schedule identifying uplink and/ordownlink transmission periods during a frame sequence for one or morenodes in a wireless network. The uplink transmissions may be scheduledafter the downlink transmissions within the frame sequence. One or morenodes having both scheduled downlink and uplink transmissions during theframe sequence may be scheduled for transmissions near a transition fromdownlink to uplink transmissions.

In yet another embodiment, a method is provided. The method may includetransmitting a frame identifying uplink and/or downlink transmissionperiods during a frame sequence for one or more nodes in a wirelessnetwork. The uplink transmissions may be scheduled after the downlinktransmissions within the frame sequence. One or more nodes having onlyscheduled downlink transmissions during the frame sequence may bescheduled for downlink transmissions at or near the start of thedownlink transmissions. One or more nodes having only scheduled uplinktransmissions during the frame sequence may be scheduled for uplinktransmissions at or near the end of the uplink transmissions. One ormore nodes having scheduled both downlink and uplink transmissionsduring the frame sequence may be scheduled for transmissions near atransition from downlink to uplink transmissions.

In another embodiment, an apparatus may be provided. The apparatus mayinclude a controller, a memory coupled to the controller. The apparatusmay be adapted to transmit a frame identifying uplink and/or downlinktransmission periods during a frame sequence for one or more nodes in awireless network. The uplink transmissions may be scheduled after thedownlink transmissions within the frame sequence. In one embodiment, oneor more nodes having only scheduled downlink transmissions during theframe sequence may be scheduled for downlink transmissions at or nearthe start of the downlink transmissions. In another embodiment, one ormore nodes having only scheduled uplink transmissions during the framesequence may be scheduled for uplink transmissions at or near the end ofthe uplink transmissions. In yet another embodiment, one or more nodeshaving scheduled both downlink and uplink transmissions during the framesequence may be scheduled for transmissions near a transition fromdownlink to uplink transmissions.

In another embodiment, an article may be provided including a storagemedium. The storage medium may include instructions stored thereon that,when executed by a processor, may result in: transmitting a frameidentifying uplink and/or downlink transmission periods during a framesequence for one or more nodes in a wireless network. The uplinktransmissions may be scheduled after the downlink transmissions withinthe frame sequence. In one embodiment, one or more nodes having onlyscheduled downlink transmissions during the frame sequence may bescheduled for downlink transmissions at or near the start of thedownlink transmissions. In another embodiment, one or more nodes havingonly scheduled uplink transmissions during the frame sequence may bescheduled for uplink transmissions at or near the end of the uplinktransmissions. In yet another embodiment, one or more nodes havingscheduled both downlink and uplink transmissions during the framesequence may be scheduled for transmissions near a transition fromdownlink to uplink transmissions.

BRIEF DESCRIPTION OF THE DRAWINGS

The details of one or more implementations are set forth in theaccompanying drawings and the description below. Other features will beapparent from the description and drawings, and from the claims.

FIG. 1 is a block diagram illustrating a wireless network according toan example embodiment;

FIG. 2 is a diagram illustrating a format of a multi poll message, suchas a Power Save Multi Poll (PSMP) management frame, according to anexample embodiment;

FIG. 3 is a diagram illustrating a PSMP sequence according to an exampleembodiment.

FIG. 4 is a timing diagram illustrating a data transmission scheduleaccording to an example embodiment;

FIG. 5 is a timing diagram illustrating a data transmission scheduleaccording to another example embodiment;

FIG. 6 is a flow chart illustrating operation of a wireless nodeaccording to an example embodiment.

FIG. 7 is a block diagram illustrating an apparatus that may be providedin a wireless node according to an example embodiment.

DETAILED DESCRIPTION

Referring to the Figures in which like numerals indicate like elements,FIG. 1 is a block diagram illustrating a wireless network according toan example embodiment. Wireless network 102 may include a number ofwireless nodes or stations, such as an access point (AP) 104 or basestation and one or more mobile stations, such as stations 106 and 108.While only one AP and two mobile stations are shown in wireless network102, any number of APs and stations may be provided. Each station innetwork 102 (e.g., stations 106, 108) may be in wireless communicationwith the AP 104, and may even be in direct communication with eachother. Although not shown, AP 104 may be coupled to a fixed network,such as a Local Area Network (LAN), Wide Area Network (WAN), theInternet, etc., and may also be coupled to other wireless networks.

The various embodiments described herein may be applicable to a widevariety of networks and technologies, such as WLAN networks (e.g., IEEE802.11 type networks), IEEE 802.16 Wi MAX networks, cellular networks,radio networks, or other wireless networks. In another exampleembodiment, the various examples and embodiments may be applied, forexample, to a mesh wireless network, where a plurality of mesh points(e.g., Access Points) may be coupled together via wired or wirelesslinks. The various embodiments described herein may be applied towireless networks, both in an infrastructure mode where an AP or basestation may communicate with a station (e.g., communication occursthrough APs), as well as an ad-hoc mode in which wireless stations maycommunicate directly via a peer-to-peer network, for example.

The term “wireless node” or “node,” or the like, may include, forexample, a wireless station, an access point (AP) or base station, awireless personal digital assistant (PDA), a cell phone, an 802.11 WLANphone, a wireless mesh point, or any other wireless device. These aremerely a few examples of the wireless devices that may be used toimplement the various embodiments described herein, and this disclosureis not limited thereto.

In an example embodiment, a wireless node (e.g., AP or station) maydetermine capabilities of other nodes by receiving a capabilities fieldin a beacon message or probe response (e.g., from an AP) and via anassociation request or re-association request (e.g., from a station),for example. An AP may associate with one or more wireless stations ornodes. The process of associating an AP with one more wireless stationsor nodes may include the AP assigning an Association ID (AID) to each ofthe wireless stations or node with which it is associated.

After a station is associated with an AP, the two nodes may establish adata transmission schedule, indicating a service period, for example, byexchanging one or more frames or messages indicating a schedule starttime for the service period. A variety of different mechanisms may beused to exchange or agree on a time for a service period. For example,the IEEE 802.11e draft specification allows for power management throughautomatic power-save delivery (APSD). APSD provides two deliverymechanisms: scheduled APSD and unscheduled APSD. Stations may useunscheduled APSD (U-APSD) to have all or some of their frames deliveredto them from the AP during unscheduled service periods. An unscheduledservice period may begin when the AP receives a trigger message from thestation. According to scheduled APSD (S-APSD), a station may receive adata transmission schedule from an AP indicating a service start timeand service interval when the station may receive and transmit framesduring scheduled service periods. For example, by using APSD, a stationmay conserve power and extend battery life by remaining in a lower powerstate, and then waking during a scheduled or unscheduled service periodto receive and transmit data. In an example embodiment, an AP mayallocate the same service period for multiple stations or nodes, whichmay require each of these multiple stations to be awake during asubstantial portion of (or even all of) the service period in somecases, as examples.

In an example embodiment, an AP or other node may transmit (e.g.,broadcast) a frame, such as an aggregation control header frame or aPower Save Multi Poll (PSMP) frame or message, or other message. ThePSMP message (or other frame) may, for example, include a datatransmission schedule identifying uplink and/or downlink transmissionperiods during a frame sequence for one or more nodes in a wirelessnetwork. Downlink may refer to transmissions from an AP or access pointor base station to stations or other nodes, while uplink may refer totransmissions from stations or other nodes to an AP or base station, forexample. In an example embodiment, a PSMP sequence may include, forexample, transmission of a PSMP message, followed by downlinktransmission of broadcast or multicast data, followed by downlinkunicast transmissions to one or more nodes, followed by uplinktransmissions from one or more nodes to the AP. Other orders may be usedfor a frame sequence or PSMP sequence.

The PSMP frame may allow an AP or a wireless node to provide schedulesor sub-schedules to each of a plurality of wireless stations or nodes.These PSMP data transmission schedules, or sub-schedules, may indicatefor example a downlink start time and duration (for a scheduledtransmission to a specified station), and/or an uplink start time andduration (for a scheduled transmission period where a specified stationmay be permitted to transmit data on the medium). The PSMP frame, whichmay include a DLT (downlink transmission) and/or ULT (uplinktransmission) schedules, may be transmitted according to the S-APSDservice period, for an U-APSD, or may be transmitted at any time (e.g.,during unscheduled periods), according to example embodiments. A PSMPframe may be transmitted by any wireless node, such as by an accesspoint (AP) or a station.

FIG. 2 is a diagram illustrating a format of a multi poll message, suchas an IEEE 802.11n Power Save Multi Poll (PSMP) management frame 200,according to an example embodiment. Management action frame 201 mayinclude a MAC header 202 that may include MAC address information andother fields, a frame body 204 and a frame check sequence (FCS) 206, forexample. In an example embodiment, frame body 204 may be a Power SaveMulti Poll (PSMP) frame body. The frame body 204 may include a categoryfield 210 set to a value indicating High Throughput (HT) (e.g., HT orIEEE 802.11n related frame), for example. Frame body 204 may alsoinclude an Action field 212 set to a value indicating a PSMP frame.

Frame body 204 may also include a PSMP parameter set 214 and one or morestation information fields (STA Info fields) 216. PSMP parameter set 214may include a number of stations (N_STA) field 215 indicating a numberof station information fields (STA Info fields) present in the framebody 204. Further, a More PSMP field 219 may be set to a 1, for example,to indicate that this PSMP sequence may typically be followed by anotherPSMP sequence. Alternatively, More PSMP 219 may be set to 0 to indicatethat this is the last PSMP sequence during this service period.According to an example embodiment, a PSMP sequence may include, forexample, a PSMP frame followed by a scheduled data transmission to(downlink) and/or from (uplink) one or more stations, as indicated bythe PSMP frame. PSMP sequence duration field 221 indicates the durationof the current PSMP sequence which is described by the PSMP frame.

As noted above, an AP may transmit to a plurality of stations and/orreceive from a plurality of stations, according to the informationprovided in the one or more station information (STA Info) fields 216,e.g., in accordance with the transmission schedule provided via one ormore STA Info fields 216. The information provided in the one or moreSTA Info fields 216 may be generally referred to as a schedule or atransmission schedule. A STA Info field may be provided for each stationfor which uplink and/or downlink transmission is being scheduled by thePSMP message (for the current PSMP sequence). The number of STA Infofields is indicated by the N_STA field 215. Therefore, the PSMP framebody 204 illustrated in FIG. 2 may include one or more STA Info fields,such as STA Info fields 216A, 216B, . . . 216Z, as an example.

Each STA Info field 216 may include a plurality of fields. The STA Infofield 216 may include a traffic stream identifier (TSID) field 223,which may identify one or more TSIDs that a station may or should usefor transmitting data back to the AP for a scheduled uplink datatransmission, for example. A station identifier (STA ID) field 225 mayidentify the station (e.g., using either a portion of a MAC address ofthe station or the AID for the station). Although not required, in anexample embodiment, the STA ID field 225 in STA Info field 216 may beset to zero to indicate a multicast transmission. In addition, STA IDfield 225 may also be set to all 1s to indicate a broadcasttransmission. The TSID field 223 and the STA ID field 225 may notnecessarily be applicable for the scheduling of a multicast transmission(e.g., upstream TSIDs not applicable for downstream multicasttransmission, and a multicast frame is typically directed to multiplereceiver nodes and thus one STA ID field would typically be inadequate,for example).

The downlink transmission (DLT) start offset field 227 may indicate astart time for the scheduled downlink data transmission (from AP tostation), and a downlink transmission (DLT) duration field 229 mayindicate a duration for the scheduled downlink transmission. These twoDLT related fields (227, 229) may be applicable for both a unicasttransmission (e.g., transmission to a single receiver node) and amulticast transmission (multicast may be, for example, a downlink datatransmission from the AP to multiple receiver nodes or stations).

An uplink transmission (ULT) (from station to AP) start offset field 231and a ULT duration field 233 are provided within the STA Info field 216to communicate a start time and duration for a scheduled uplink datatransmission for a node or station.

FIG. 3 is a diagram illustrating a PSMP sequence according to an exampleembodiment. In FIG. 3, a PSMP sequence 301 may include the transmissionof a PSMP frame 302, followed by a scheduled downlink broadcast and/ormulticast data transmission period 309 to one or more receiver nodes, ascheduled downlink unicast data transmission period 311 to one or morereceiver nodes, and a scheduled uplink unicast transmission period 315from one or more receiver nodes, for example. In an example embodiment,the uplink transmissions (315) may be scheduled after the downlinktransmissions (309 and/or 311). A transition 317 is shown from downlinktransmissions (DLT) (e.g., 309, 311) to uplink transmissions (ULT) 315.The transition from DLT to ULT may be a point, for example, afterdownlink transmissions (e.g., 309, 311) for the PSMP sequence 301 arecompleted, and just before the uplink transmissions (315) for thesequence 301 have begun.

In the PSMP frame 302, the TSID field 223 may indicate a traffic streamfor which a receiver node may transmit frames during the scheduleduplink unicast data transmission period 315, for example. The STA IDfield 225 may include the AID for the receiver node (or otherwiseidentify the receiver node). The DLT fields 227 and 229 may be set tovalues indicating a start time and duration, respectively, for thescheduled downlink unicast data transmission period 311 to theidentified receiver node. Likewise, the ULT fields 231 and 233 withinPSMP frame 302 may be set to values indicating the start time andduration, respectively, for the scheduled uplink unicast datatransmission that is being provided to the identified receiver node(e.g., identified by STA ID).

After transmitting the PSMP frame 302, the AP may immediately orsubstantially immediately (e.g., without intervening frames) transmitone or more downlink frames as part of the DLTs. For example, the AP mayimmediately after the PSMP frame 302, may transmit one or more broadcastand/or multicast frames (304, 306, . . . ) for the scheduled downlinkbroadcast/multicast data transmission period 309. Thus, according to anexample embodiment, as a default scheduling time, the downlink broadcastand/or multicast data frames may be transmitted immediately aftertransmission of the PSMP frame 302, for example, so that each receivernode may know or expect the broadcast and/or multicast datatransmissions at this time. In an example embodiment, broadcast dataframes may be scheduled prior to multicast data frames. In anotherembodiment, multicast data frames may be scheduled prior to broadcastdata frames. In yet another embodiment, the scheduling of broadcast dataframes and multicast data frames may be interspersed with one another.

In the case of multicast transmissions, a dedicated STA Info field 216can be used to indicate multicast transmission(s). In this case, theTSID field 223 may be set to 1 or other specific value to indicate thatthe receiver nodes which have scheduled uplink transmissions shall sendmulticast acknowledgement(s) back. In this situation, the STA ID field225 may be set to 0. In an example embodiment, for broadcast/multicasttransmissions, the DLT fields 227 and 229 may be used to communicatedownlink multicast transmission period(s) or schedule and the ULT fields231 and 233 may be set to 0 (or don't cares). However, these are merelyexamples, and the various embodiments are not limited thereto.

In an example embodiment, if there are no downlink broadcast/multicastframes to be transmitted from the AP for this PSMP sequence, thescheduled downlink unicast data transmissions 311 may begin after thePSMP frame, for example. Or, in another embodiment, the downlink unicasttransmissions (311) may begin after the PSMP frame andbroadcast/multicast downlink transmissions (309) may come after downlinkunicast transmissions (311), for example.

Next, referring to FIG. 3, one or more unicast frames (e.g., frames 308,310, 312, 314) may be transmitted to and from one or more receiver nodes(e.g. “node 1,” “node 2” and “node 3”) as part of the scheduled downlinkunicast data transmission period 311 and the scheduled uplink unicastdata transmission period 315. In the situation where the unicast framesare being transmitted to and/or from PSMP capable stations (e.g., “node1,” “node 2” and “node 3” in this embodiment), the transmission ofunicast frames may be scheduled in the PSMP frame so as to reduce thenumber of on/off transitions for the PSMP cable capable stations duringthe PSMP sequence 301, and/or to increase a delay between a node's DLTand ULT periods. By scheduling DLT and ULT periods for nodes in thismanner may reduce the amount of “awake time” (e.g., the amount of timeoperating in a full power mode) for PSMP capable stations during a givenPSMP sequence. Accordingly, power consumption for PSMP capable stationsmay be reduced using the scheduling techniques described below, forexample. In general, a DLT may be a period when a station or node mayreceive data, either from an AP or other station. A ULT is a period whena station may transmit data over the medium to an AP or other station.

An on/off transition may, for example, be a transition from an operatingmode (e.g., full power mode) to a low power (e.g., standby/sleep mode)and vice versa. For purposes of this disclosure, an on/off transitionmay refer interchangeably to (i) a transition from an operating mode toa standby mode and (ii) a transition from a standby mode to an operationmode. By scheduling transmission of frames in accordance with theembodiments described herein, the number of on/off transitions for PSMPstations may be reduced. Likewise, the amount of time such PSMP stationsare in low power (e.g., standby mode) may be increased by schedulingtransmission of unicast frames in accordance with the embodimentsdescribed herein.

In the example embodiment illustrated in FIG. 3, three PSMP stations(node 1, node 2 and node 3) have unicast frames scheduled fortransmission during PSMP sequence 301. For instance, in this example,node 1 only has only a scheduled transmission of downlink unicast frame308, while node 3 only has a scheduled transmission of only uplinkunicast frame 314. Node 2, in comparison, has a scheduled transmissionof downlink unicast frame 310 and uplink unicast frame 312 scheduled.This is merely an illustrative or example embodiment. Other embodimentsexist where additional nodes or fewer nodes are scheduled for datatransmissions or additional frames may be transmitted. Further, it willbe appreciated that the types of data scheduled for transmission toand/or from a given node and the schedules for those transmissions mayvary from PSMP sequence to PSMP sequence.

According to an example embodiment, for one or more nodes having onlyscheduled downlink transmissions during a PSMP sequence, these nodes maybe scheduled for downlink transmissions at or near the start of thedownlink transmissions 311. For example, as is shown in FIG. 3,transmission of downlink unicast frame 308 for node 1 is scheduled at ornear the beginning of the downlink unicast data transmission period 311.Although not required, the downlink transmission may be scheduledsubstantially immediately after the PSMP frame 302 or after thebroadcast/multicast transmissions 309. In this situation, node 1 mayenter a low power state for the remainder of the PSMP sequence 301 afterunicast frame 308 has been received. In an example embodiment, node 1may be operating in a full power mode (awake) during broadcast/multicastdata transmission period 309, receive its downlink transmissions (e.g.,frame 308), and then enter low power state.

By scheduling transmission of unicast frame 308 at or near the beginningof downlink unicast transmission period 311, the number of on/offtransitions as well as the amount of time node 1 spends awake may bereduced. For instance, delaying the downlink transmission of frame 308for node 1 until the middle or end of DLT 311 may typically increase theperiod of time that node 1 is operating in full power mode, therebytypically increasing power consumption for node 1. Alternatively node 1may go through an additional on/off transition, for example, going intostandby mode after broadcast/multicast data transmission period 309 andreturning to an awake (full power) mode at or just prior to thescheduled downlink unicast transmission of unicast frame 308. However,such an approach may, for example, be less power-efficient in some casesthan scheduling the DLT (e.g., frame 308) for node 1 at or near thebeginning of the downlink transmissions 311.

According to another example embodiment, for one or more nodes havingonly scheduled uplink transmissions during a PSMP sequence, these nodesmay be scheduled for uplink transmissions at or near the end of theuplink transmissions 315. For example, node 3 is scheduled only foruplink data transmissions (e.g., frame 314). Therefore, transmission ofuplink unicast frame 314 for node 3 may be scheduled at or near the endof the uplink unicast data transmission period 315. In this situation,node 3 may enter a low power state after the broadcast/multicast datatransmission period 309 and remain in the low power state during theunicast data transmission periods 311, until returning to full-powermode at or just prior to the scheduled uplink unicast transmission ofunicast frame 314. Node 3 may then transmit frame 314, and then returnto low power state until it is time to receive the next PSMP frame, forexample. In another example embodiment, node 3 may enter the low powerstate after receiving PSMP frame 302 if there is no data scheduled to betransmitted to node 3 during the broadcast/multicast data transmissionperiod 309 of PSMP sequence 301, or if there are no broadcast ormulticast frames to be transmitted.

By scheduling transmission of unicast frame 314 (for node 3, scheduledonly for uplink transmissions) at or near the end of uplink unicasttransmission period 315, the number of on/off transitions as well as theamount of time node 3 spends awake (or in full power mode) may bereduced, at least in some cases. For instance, if node 3 were scheduledfor uplink transmissions at the beginning of uplink transmissions 315,this may reduce the amount of time that node 3 spends in a low powerstate. Also, if the time between on/off transitions is sufficient enoughfor a node to transition to a lower power STA than standby (or lowpower) state and back to active state (before it needs to be awake),then a node can transition to a lower power or deep sleep state and saveadditional power.

In an example embodiment, node 3 may go through multiple additionalon/off transitions, for example, going into standby mode afterbroadcast/multicast data transmission period 309 and returning to anawake (full power) mode at or just prior to the scheduled uplink unicasttransmission of unicast frame 314 and then returning to low power modeafter sending unicast frame 314. Node 3 would then go through anotheron/off transition at or just prior to the transmission of a next PSMPframe 321. Using the approach illustrated in FIG. 3, because node 3transmits the unicast packet 314 at or near the end of uplinktransmission period 315, it may remain awake to receive the next PSMPframe 321, thus reducing the number of on/off transitions. This isanother example embodiment.

In yet another example embodiment, for nodes scheduled for both (e.g.,unicast) downlink and uplink transmissions during a PSMP sequence, thesenodes may be scheduled for transmissions near or around a transition 317from downlink transmissions to uplink transmissions. For example, asshown in FIG. 3, node 2 is scheduled for both unicast downlinktransmissions and uplink transmissions during PSMP sequence 301.Therefore, the transmission of downlink unicast frame 310 andtransmission of uplink unicast frame 312 for node 2 may be scheduled ator near (or around) the transition between downlink unicast datatransmission period 311 and uplink unicast data transmission period 315.In this situation, node 2 may, for example, enter a low power stateafter the broadcast/multicast data transmission period 309 (or afterreceiving the PSMP frame 302 if no broadcast or multicast datatransmissions are scheduled) and remain in the low power state duringmost of the unicast down link data transmission period 311 untilreturning to an awake (full power) mode at or just prior to thescheduled downlink unicast transmission of unicast frame 310 at or nearthe end of downlink unicast transmission period 311. Node 2 may thenremain awake and transmit uplink unicast frame 312 at or near thebeginning of uplink unicast data transmission period 315.

By scheduling the transmission of downlink unicast frame 310 at or nearthe end of downlink unicast transmission period 311 and scheduling thetransmission of uplink unicast frame 312 at or near the beginning ofuplink unicast transmission period 315, the number of on/off transitionsas well as the amount of time node 2 spends awake may be reduced, atleast in some cases. For instance, were the transmission of downlinkunicast packet 310 scheduled at the middle or near the beginning of thedownlink unicast data transmission period 311 and the transmission ofuplink unicast packet 312 scheduled at the middle or near the end of theuplink unicast data transmissions, node 2 may remain on for a longerperiod of time (e.g., before and/or after the scheduled transmissions)during part of which it may be idle (e.g., not transmitting or receivingdata).

Alternatively, in the above situation, node 2 may go through multipleadditional on/off transitions, for example, going into standby modeafter broadcast/multicast data transmission period 309 (or afterreceiving PSMP frame 302) and returning to an awake (full power mode) ator just prior to the scheduled downlink unicast transmission of unicastframe 310. Node 2 may then return to low power mode after receivingunicast frame 310 and then return to the awake (full power) mode at orjust prior to the scheduled uplink unicast transmission of unicast frame312. Further, node 2 may return to low power mode after transmittingunicast frame 314. Node 2, in this situation, may go through yet anotheron/off transition at or just prior to the transmission of a next PSMPframe 321. Using the approach illustrated in FIG. 3, because node 3receives the unicast packet 310 and transmits the unicast packet 312 ator near the transition between downlink transmission period 311 anduplink transmission period 315, node 2 may simply remain awake afterreceiving unicast packet 310 to transmit unicast packet 312, thusreducing the number of on/off transitions.

FIG. 4 is a timing diagram that illustrates an example embodiment of adata transmission schedule for a downlink transmission time period (DLT)404 and an uplink transmission time period (ULT) 406 for an example PSMPsequence. The data transmission schedule illustrated FIG. 4 may beincluded in a frame (e.g., management frame), such as a PSMP frame 402.A transition point 408 in FIG. 4 designates the transition between DLT404 and ULT 406 for the example data transmission schedule. For theschedule shown in FIG. 4, scheduling of broadcast and/or multicast datais not illustrated. It will be appreciated, however, that such aschedule may include scheduling of broadcast and/or multicast in asimilar fashion as described above with respect to FIG. 3.

The data transmission schedule illustrated in FIG. 4 is similar to thePSMP sequence 301 illustrated in FIG. 3. In comparison, the datatransmission schedule in FIG. 4 includes an additional node for whichdata transmission periods (downlink and uplink) are scheduled duringboth DLT 404 and ULT 404, as was the case with node 2 in FIG. 3.Accordingly, the data transmission schedule of FIG. 4 illustrates a datatransmission schedule for four PSMP capable stations, PSTA 1, PSTA 2,PSTA 3 and PSTA 4. As was noted above, such a data transmission schedulemay also include scheduling of data transmissions for non-PSMP stations.However, for the sake of clarity, scheduling of data transmissions fornon-PSMP stations is not shown.

For the PSMP sequence of FIG. 4, PSTA 1 has only downlink unicast datatransmissions scheduled during DLT 404, PSTA 2 has only uplink unicastdata transmissions scheduled during ULT 406, and PSTAs 3 and 4 have bothdownlink and uplink unicast data transmissions scheduled (during DLT 404and ULT 406). As illustrated in FIG. 4, PSTAs 1-4 may all be awakeduring the time period when PSMP frame 402 is being communicated. Afterreceiving the PSMP frame 402, the PSTAs 1-4 may then operate inaccordance with the data transmission schedule illustrated in FIG. 4,which may be included in the PSMP frame 402. The data transmissionschedule for each PSTA will be described in turn.

As noted above, PSTA 1 only has downlink unicast data transmission(s)scheduled during the PSMP sequence illustrated in FIG. 4. The downlinkunicast data transmission(s) for PSTA 1 are scheduled at or near thebeginning of DLT 404. Accordingly, PSTA 1, during a time period 410,remains awake after receiving the PSMP frame 402 to receive thescheduled downlink transmission(s). Once the downlink transmissions forPSTA 1 are complete at the end of time period 410, PSTA 1 may enterstandby (sleep) mode for the time period 412, which may include theremainder of the illustrated PSMP sequence. As discussed above, such anapproach may reduce the number of on/off transitions for PSTA 1 and alsomay increase the amount of time PSTA 1 spends in standby. This can allowa PSTA to transition to a lower power consuming state than standby(e.g., deep sleep) and transition back to active state before the nodeneeds to be awake. This provides additional power savings to the PSTA.

In FIG. 4, as discussed above, PSTA 2 only has uplink unicast datatransmission(s) scheduled during the PSMP sequence illustrated in FIG.4. The uplink unicast data transmission(s) for PSTA 1 are scheduled ator near the end of ULT 406. Accordingly, PSTA 2, after a time period 414during which PSTA 2 receives PSMP frame 402, enters standby mode andremains until just before its scheduled uplink unicast datatransmission(s). For instance, during a time period 418, PSTA 2 wakes up(e.g., transitions from standby to full power mode). PSTA 2 thencompletes its scheduled uplink unicast data transmissions during a timeperiod 420. Once the uplink transmissions for PSTA 2 are complete at theend of time period 420, PSTA 2 may remain awake to receive a next PSMPframe. Alternatively, PSTA 2 may enter standby (sleep) mode if furtherPSMP sequences do not occur. As discussed above, such an approach mayreduce the number of on/off transitions for PSTA 2 and also may increasethe amount of time PSTA 2 spends in standby.

Further in FIG. 4, as noted above, PSTAs 3 and 4 both have downlinkunicast data transmission periods and uplink unicast data transmissionperiods scheduled during DLT 404 and ULT 406. As shown in FIG. 4, thedownlink unicast data transmission(s) for PSTAs 3 and 4 may be scheduledat or near the end of DLT 404 (e.g., just before transition point 408)while the uplink unicast data transmission(s) may be scheduled at ornear the beginning of ULT 406 (e.g., just after transition point 408).

PSTA 3 in FIG. 4, after a time period 422 during which PSTA 3 receivesPSMP frame 402, may enter standby mode and remain in standby mode duringa time period 424 until just before its scheduled downlink unicast datatransmission period. For instance, during a time period 426, PSTA 3wakes up (e.g., transitions from standby to full power mode). PSTA 3then completes its scheduled downlink unicast data transmission(s)during a time period 428. The uplink transmission(s) period for PSTA 3is discussed below.

In like fashion as PSTA 3, PSTA 4 in FIG. 4 receives the PSMP frame 402during a time period 434. Once PSTA 4 receives the PSMP from 402, it mayenter standby mode and remain in standby mode during a time period 436until just before its scheduled downlink unicast data transmissionperiod. For instance, during a time period 438, PSTA 4 wakes up (e.g.,transitions from standby to full power mode). PSTA 4 then completes itsscheduled downlink unicast data transmission(s) during a time period440.

As shown in FIG. 4, transition point 408 occurs during time period 440.Accordingly, PSTA 4 may remain awake after competing its scheduleddownlink unicast transmission(s) and also complete its scheduled up linktransmission(s) during the time period 440. Once the uplinktransmissions for PSTA 4 are complete at the end of time period 440,PSTA 4 may enter standby (sleep) mode for the time period 437, which mayinclude the remainder of the illustrated PSMP sequence.

For the example embodiment shown in FIG. 4, PSTA 3 completes its uplinktransmission(s) during a time period 432. Time period 432 occurssubstantially immediately after time period 440, during which PSTA 4 maycomplete its uplink and downlink unicast transmissions. Such anarrangement allows for scheduling of data transmissions for PSTAs thathave both scheduled downlink and uplink unicast data transmissionperiods during a given PSMP sequence. PSTA 3 may remain active during atime period 430 (between its scheduled downlink transmission time period428 and its scheduled uplink unicast data transmission time period 432.Alternatively, PSTA 3 may enter standby (sleep) mode during time period430. Once the uplink transmissions for PSTA 3 are complete at the end oftime period 432, PSTA 3 may enter standby (sleep) mode for the timeperiod 425, which may include the remainder of the illustrated PSMPsequence. Using the approach shown in FIG. 4 (e.g., scheduling downlinkand uplink unicast data transmissions periods for PSTAs which have bothdownlink and uplink unicast data transmissions in a given PSMP sequenceso that the time periods bridge transition point 408) may reduce thenumber of on/off transitions for such PSTAs, as well as increase theamount of time such PSTAs spend in standby (sleep) mode.

FIG. 5 is a timing diagram that illustrates an alternative exampleembodiment of a data transmission schedule for scheduling downlink anduplink unicast data transmissions periods for PSTAs which have bothdownlink and uplink unicast data transmissions in a given PSMP sequence.In similar fashion as the data transmission schedule of FIG. 4, theschedule of FIG. 5 includes a downlink transmission time period (DLT)504 and an uplink transmission time period (ULT) 506 for an example PSMPsequence. The schedule of FIG. 5 may be included in a frame (e.g.,management frame), such as a PSMP frame 502. As with FIG. 4, atransition point 508 in FIG. 5 designates the transition between DLT 504and ULT 506 for the example data transmission schedule. Also for theschedule shown in FIG. 5, scheduling of broadcast and/or multicast datais not illustrated. It will be appreciated, however, that such aschedule may include scheduling of broadcast and/or multicast in asimilar fashion as described above with respect to FIG. 3.

FIG. 5 illustrates a data transmission schedule for two PSMP capablestations, PSTA 1 and PSTA 2, which, as noted above, both have scheduleddownlink and uplink unicast data transmission periods for the particularPSMP sequence illustrated. Each PSTA in FIG. 5 will be discussed inturn. In an example embodiment illustrated in FIG. 5, nodes or stationsthat may be scheduled for both downlink and uplink transmissions may bescheduled for downlink transmissions at or near the beginning of thedownlink transmission (DLT) period 504, and may be scheduled for uplinktransmissions at or near the end of the uplink transmission (ULT) period506. In this manner, the number of on/off transitions may be decreasedand the period of time a stations or node operates in full power modemay be decreased.

PSTA 1 in FIG. 5 may be awake (operating in a full power mode) during atime period 510. During time period 510, PSTA 1 may receive PSMP header502. Also during time period 510 (e.g., substantially immediately afterreceiving the PSMP header 502), PSTA 1 make receive its scheduleddownlink unicast data transmission. After completing the scheduleddownlink unicast data transmission, PSTA 1 may enter standby mode untiljust before its scheduled uplink unicast data transmission time period516. For instance, during a time period 514, PSTA 1 wakes up (e.g.,transitions from standby to full power mode). PSTA 1 then completes itsscheduled uplink unicast data transmission(s) during time period 516.Once the uplink unicast transmissions for PSTA 1 are complete at the endof time period 516, PSTA 1 may remain awake to receive a next PSMPframe. Alternatively, PSTA 1 may enter standby (sleep) mode if furtherPSMP sequences do not occur.

In like fashion as PSTA 1 in FIG. 5, PSTA 2 in FIG. 5 may be awake(operating in a full power mode) during a time period 518. During timeperiod 518, PSTA 2 may receive PSMP header 502. PSTA 2 may then enterstandby mode during a time period 520 (which may correspond with theremainder of time period 510) while PSTA 1 of FIG. 5 is completing itsscheduled downlink unicast data transmission. Alternatively, PSTA 2 inFIG. 5 may remain awake during time period 520 and wake just before itsscheduled downlink unicast data transmission time period 522. Aftercompleting its scheduled downlink unicast data transmission, PSTA 2 mayenter standby mode until just before its scheduled uplink unicast datatransmission time period 528. For instance, during a time period 526,PSTA 2 wakes up (e.g., transitions from standby to full power mode).PSTA 2 then completes its scheduled uplink unicast data transmission(s)during time period 528. Once the uplink unicast transmissions for PSTA 2are complete at the end of time period 528, PSTA 2 may remain awake toreceive a next PSMP frame (not shown in FIG. 5). Alternatively, PSTA 2may enter standby (sleep) mode until the end of the PSMP sequenceillustrated in FIG. 5.

FIG. 6 is a flow chart illustrating operation of a wireless nodeaccording to an example embodiment. At 610, the node, such as a basestation or AP (as examples), may transmit a frame identifying uplinkand/or downlink transmission periods during a frame sequence for one ormore nodes in a wireless network. The uplink transmissions may bescheduled after the downlink transmissions within the frame sequence.The flow chart of FIG. 6 may include one additional operations 620, 630and/or 640.

At 620, one or more nodes having only scheduled downlink transmissionsduring the frame sequence may be scheduled for downlink transmissions ator near the start of the downlink transmissions. At 630, one or morenodes having only scheduled uplink transmissions during the framesequence may be scheduled for uplink transmissions at or near the end ofthe uplink transmissions. At 640, one or more nodes having scheduledboth downlink and uplink transmissions during the frame sequence may bescheduled for transmissions near a transition from downlink to uplinktransmissions. Data frames may then be transmitted according to the datatransmission schedule included in the PSMP frame, e.g., downlinktransmission, followed by uplink transmissions, according to theschedule.

FIG. 7 is a block diagram illustrating an apparatus 700 that may beprovided for wireless communications, e.g., in a wireless node accordingto an example embodiment. The wireless node (e.g. station or AP) mayinclude, for example, a wireless transceiver 702 to transmit and receivesignals, a controller 704 to control operation of the station andexecute instructions or software, and a memory 706 to store data and/orinstructions.

When a wireless node receives a management frame such as, for example,the PSMP frame illustrated in FIG. 2, the node may determine whether itis to receive unicast traffic, multicast and/or broadcast traffic basedon the schedules determined by the PSMP frame 200. Such schedules may beimplemented, for example, in accordance with the embodiments describedabove. If a determination is made that no traffic is destined to be sentto or from the wireless station, the wireless station can conserve powerand enter a low power state for a current frame sequence afterreceiving, for example, such a PSMP header.

Controller 704 may be programmable and capable of executing software orother instructions stored in memory or on other computer media toperform the various tasks and functions described above. For example,controller 704 may be programmed to transmit a management frame, such asa PSMP frame, to identify a scheduled data transmission time(s) anddirection(s) for each of one or more receiver nodes in a wirelessnetwork.

In an example embodiment, controller 704 or apparatus 700 may transmit aframe identifying uplink and/or downlink transmission periods during aframe sequence for one or more nodes in a wireless network. The uplinktransmissions may be scheduled after the downlink transmissions withinthe frame sequence. In one embodiment, one or more nodes having onlyscheduled downlink transmissions during the frame sequence may bescheduled for downlink transmissions at or near the start of thedownlink transmissions. In another embodiment, one or more nodes havingonly scheduled uplink transmissions during the frame sequence may bescheduled for uplink transmissions at or near the end of the uplinktransmissions. In yet another embodiment, one or more nodes havingscheduled both downlink and uplink transmissions during the framesequence may be scheduled for transmissions near a transition fromdownlink to uplink transmissions.

In addition, a storage medium may be provided that includes storedinstructions, when executed by a controller or processor that may resultin the controller 704, or other controller or processor, performing oneor more of the functions or tasks described above.

Implementations of the various techniques described herein may beimplemented in digital electronic circuitry, or in computer hardware,firmware, software, or in combinations of them. Implementations mayimplemented as a computer program product, i.e., a computer programtangibly embodied in an information carrier, e.g., in a machine-readablestorage device or in a propagated signal, for execution by, or tocontrol the operation of, data processing apparatus, e.g., aprogrammable processor, a computer, or multiple computers. A computerprogram, such as the computer program(s) described above, can be writtenin any form of programming language, including compiled or interpretedlanguages, and can be deployed in any form, including as a stand-aloneprogram or as a module, component, subroutine, or other unit suitablefor use in a computing environment. A computer program can be deployedto be executed on one computer or on multiple computers at one site ordistributed across multiple sites and interconnected by a communicationnetwork.

Method steps may be performed by one or more programmable processorsexecuting a computer program to perform functions by operating on inputdata and generating output. Method steps also may be performed by, andan apparatus may be implemented as, special purpose logic circuitry,e.g., an FPGA (field programmable gate array) or an ASIC(application-specific integrated circuit).

While certain features of the described implementations have beenillustrated as described herein, many modifications, substitutions,changes and equivalents will now occur to those skilled in the art. Itis, therefore, to be understood that the appended claims are intended tocover all such modifications and changes as fall within the true spiritof the various embodiments.

1. A method comprising: transmitting, by an apparatus to at least afirst node, a second node, and a third node, a frame identifying uplinkand downlink transmission periods, at least one downlink start time andduration for the first node, at least one downlink start time andduration for the second node, at least one uplink start time andduration for the second node, and at least one uplink start and durationfor the third node, during a frame sequence for at least the first node,the second node, and the third node in a wireless network, all of theuplink transmissions being scheduled after all of the downlinktransmissions within the frame sequence, with the first node having onlyscheduled downlink transmissions during the frame sequence having itsdownlink start time for downlink transmissions scheduled at or near thestart of the downlink transmissions, and with the third node having onlyscheduled uplink transmissions during the frame sequence having itsuplink start time for uplink transmissions scheduled at or near the endof the uplink transmissions, and with the second node having scheduledboth downlink and uplink transmissions during the frame sequence havingits downlink start time and its uplink start time for transmissionsscheduled near a transition from downlink to uplink transmissions. 2.The method of claim 1 wherein transmitting a frame comprisestransmitting a Power Save Multi Poll frame.
 3. The method of claim 1,wherein the frame includes the schedule identifying uplink and downlinktransmission periods, the first node entering a low power state for aremainder of the frame sequence after the duration for the first nodeand the third node entering a low power state after the frame includingthe schedule and leaving the low power state before the uplink starttime for the third node.
 4. An apparatus comprising: a controllerconfigured to transmit, to at least a first node and a second node, aframe including a schedule identifying uplink and downlink transmissionperiods, at least one downlink start time and duration for the firstnode, and at least one uplink start time and duration for the secondnode, during a frame sequence for at least the first node and the secondnode in a wireless network, all of the uplink transmissions beingscheduled after all of the downlink transmissions within the framesequence, with the first node having only scheduled downlinktransmissions during the frame sequence; wherein the scheduled downlinktransmissions for the first node having only scheduled downlinktransmissions are scheduled at or near a start of the downlinktransmissions.
 5. The apparatus of claim 4 wherein: the controller isconfigured to transmit the frame to at least the first node, the secondnode, and a third node, the second node having only scheduled uplinktransmissions has its uplink start time scheduled at or near an end ofthe uplink transmissions, and the third node having both downlink anduplink transmissions has its uplink start time and downlink start timescheduled for transmissions near a transition from downlink to uplinktransmissions.
 6. The apparatus of claim 4 wherein the controller isconfigured to transmit the frame, the frame comprising an IEEE 802.11nPower Save Multi Poll frame.
 7. The apparatus of claim 4, wherein thefirst node having only scheduled downlink transmissions during the framesequence has its downlink start time for a downlink transmissionscheduled immediately after receipt of the frame.
 8. The apparatus ofclaim 4, wherein the second node having only scheduled uplinktransmissions has its uplink start time schedule at or near an end ofthe uplink transmissions.
 9. The apparatus of claim 4, wherein thecontroller is further configured to transmit one or more downlink dataframes to at least the first node at the scheduled transmission periods.10. A first node comprising: a controller configured to receive a framefrom an access point and execute instructions included in the frame, theframe including a schedule identifying uplink and downlink transmissionperiods, at least one downlink start time and duration for the firstnode, and at least one uplink start time and duration for a second node,during a frame sequence for at least the first node and the second nodein a wireless network, all of the uplink transmissions being scheduledafter all of the downlink transmissions within the frame sequence, withthe first node having only scheduled downlink transmissions during theframe sequence; wherein the first node has its downlink start timescheduled at or near a start of the downlink transmissions.
 11. Thefirst node of claim 10, wherein the controller is configured to receivethe frame, the frame comprising transmitting a Power Save Multi Pollframe.
 12. A method comprising: receiving, by first node from anapparatus, a frame identifying uplink and downlink transmission periods,at least one downlink start time and duration for the first node, atleast one downlink start time and duration for a second node, at leastone uplink start time and duration for the second node, and at least oneuplink start and duration for a third node, during a frame sequence forat least the first node, the second node, and the third node in awireless network, all of the uplink transmissions being scheduled afterall of the downlink transmissions within the frame sequence, with thefirst node having only scheduled downlink transmissions during the framesequence having its downlink start time for downlink transmissionsscheduled at or near a start of the downlink transmissions, and with thethird node having only scheduled uplink transmissions during the framesequence having its uplink start time for uplink transmissions scheduledat or near an end of the uplink transmissions, and with the second nodehaving scheduled both downlink and uplink transmissions during the framesequence having its downlink start time and its uplink start time fortransmissions scheduled near a transition from downlink to uplinktransmissions.
 13. The method of claim 12 wherein receiving the framecomprises receiving a Power Save Multi Poll frame.
 14. The method ofclaim 12, wherein the frame includes the schedule identifying uplink anddownlink transmission periods, the first node entering a low power statefor a remainder of the frame sequence after the duration for the firstnode and the third node entering a low power state after receiving theframe including the schedule and leaving the low power state before theuplink start time for the third node.
 15. An apparatus comprising: acontroller configured to transmit, to at least a first node, a secondnode, and a third node, a frame identifying uplink and downlinktransmission periods, at least one downlink start time and duration forthe first node, at least one downlink start time and duration for thesecond node, at least one uplink start time and duration for the secondnode, and at least one uplink start and duration for the third node,during a frame sequence for at least the first node, the second node,and the third node in a wireless network, all of the uplinktransmissions being scheduled after all of the downlink transmissionswithin the frame sequence, with the first node having only scheduleddownlink transmissions during the frame sequence having its downlinkstart time for downlink transmissions scheduled at or near a start ofthe downlink transmissions, and with the third node having onlyscheduled uplink transmissions during the frame sequence having itsuplink start time for uplink transmissions scheduled at or near an endof the uplink transmissions, and with the second node having scheduledboth downlink and uplink transmissions during the frame sequence havingits downlink start time and its uplink start time for transmissionsscheduled near a transition from downlink to uplink transmissions. 16.The apparatus of claim 15 wherein the frame comprises a Power Save MultiPoll frame.
 17. The apparatus of claim 15, wherein the frame includesthe schedule identifying uplink and downlink transmission periods, thefirst node entering a low power state for a remainder of the framesequence after the duration for the first node and the third nodeentering a low power state after the frame including the schedule andleaving the low power state before the uplink start time for the thirdnode.
 18. A first node comprising: a controller configured to receive,from an apparatus, a frame identifying uplink and downlink transmissionperiods, at least one downlink start time and duration for the firstnode, at least one downlink start time and duration for a second node,at least one uplink start time and duration for the second node, and atleast one uplink start and duration for a third node, during a framesequence for at least the first node, the second node, and the thirdnode in a wireless network, all of the uplink transmissions beingscheduled after all of the downlink transmissions within the framesequence, with the first node having only scheduled downlinktransmissions during the frame sequence having its downlink start timefor downlink transmissions scheduled at or near a start of the downlinktransmissions, and with the third node having only scheduled uplinktransmissions during the frame sequence having its uplink start time foruplink transmissions scheduled at or near the end of the uplinktransmissions, and with the second node having scheduled both downlinkand uplink transmissions during the frame sequence having its downlinkstart time and its uplink start time for transmissions scheduled near atransition from downlink to uplink transmissions.
 19. The first node ofclaim 18 wherein receiving the frame comprises receiving a Power SaveMulti Poll frame.
 20. The first node of claim 18, wherein the frameincludes the schedule identifying uplink and downlink transmissionperiods, the first node entering a low power state for a remainder ofthe frame sequence after the duration for the first node and the thirdnode entering a low power state after receiving the frame including theschedule and leaving the low power state before the uplink start timefor the third node.